Preheat Gas Grill to Medium. Slice top off of 1 head of garlic and drizzle with 1 tablespoon olive oil. Place in foil and set on grill to the side for25-30 minutes. Meanwhile, slice portabellas in half, forming a thin sliced top to grill (the size of the bun). Drizzle with remaining 2 tablespoons of olive oil and sprinkle with garlic powder and white pepper on each side. Finely chop enough remaining mushroom parts for 1 Cup chopped mushrooms. Mix chopped mushrooms, ground beef, bread crumbs and minced garlic. Form 6 patties. Finely chop jalapeno and set aside. Remove roasted garlic from grill and squeeze soft garlic cloves into medium sauce pan, being careful not to get any skin in the pan. Place beef patties on grill and cook 8 minutes on each side. While patties are grilling, place medium saucepan on grill and add, to the roasted garlic, the alfredo sauce, chopped jalapeno and grated parmesan. Simmer for ten minutes, stirring occasionally, until thickened. Place portabella slices on grill. Cook for 2 minutes on each side and remove and cover to keep warm. Remove burgers and cover to keep warm. Add wheat buns to grill and toast for 3 minutes. Assemble burger: Place several slices of onion on the bottom of each bun. Next, place one leaf of lettuce. Place patties on top of lettuce. Top patties with grilled mushroom slices. Top with Jalapeno Alfredo Sauce and top bun. Serve immediately.